Microfluidic devices comprising a microfluidic structure, such as a flow channel are well known. Such microfluidic devices are often used for performing tests of fluidic samples, such as of biological fluids e.g. for performing blood tests, such a coagulation tests e.g. for determining the coagulation rate in a blood sample or agglutination tests e.g. for determining blood type of a blood sample.
In particular such microfluidic devices are used for performing tests on biological liquids.
Such devices normally depend totally or partly on capillary forces to drive a liquid into a channel of the device. Alternatively or additionally external forces may be applied to drive a liquid in the channel(s). The geometry of the channels is often very important. External forces which may be applied to fill the flow channel(s) may for example be centrifugal forces, pumping forces and similar.
Microfluidic devices of this kind are used for performing test of liquid samples. Often it is desired to subject the liquid to various treatments in the microfluidic device, e.g. mixing with other components, dissolving a reagent and optionally allowing the liquid sample to react with a reagent. It is therefore normally desired that the microfluidic device comprises some means for controlling the flow of the liquid sample along the flow path.
U.S. Pat. No. 6,575,188 discloses a microfluidic device comprising a temperature controlled valve. The microfluidic device comprises a thermally responsive substance in its passage which substance can obstruct and open the passage in relation to actuation of a heat source.
US 2003/0196714 discloses a microfluidic device including a bubble valve for regulating a fluid flow through a micro channel. The bubble valve includes a fluid meniscus interfacing the micro channel interior and an actuator for deflecting the membrane into the micro channel interior to regulate the fluid flow. The actuator generates a gas bubble in a liquid in the micro channel when a sufficient pressure is generated on the membrane.
US 2004/0206408 discloses a microfluidic device with a switch for stopping a liquid flow during a time interval. The microfluidic device comprises a capillary stop e.g. provided by a sudden change of the geometrical properties. Similar devices with capillary stops are e.g. disclosed in U.S. Pat. Nos. 6,637,463 and 6,591,852.
U.S. Pat. No. 5,230,866 discloses a microfluidic device with a capillary stop-flow junction comprising means for trapping a gas in the capillary passageway to establish a back-pressure to stop the flow in said passageway. When this means for trapping a gas is removed, the gas can continue to flow.